How does turning on a cars headlights before starting the engine help in cold weather?
I’m quite sure that the routine is to turn off lights before starting. Then again the Swedish cars in Sweden have the headlights on the moment you switch on the ignition. A set of headlight would be rated at least 55 watts X2. So that is quite a bit of power going to the lights. The starter would need at least 100amps minimum to crank from dead start and the amp would then load fall, when it spins. Even than, you need a mighty lot of amps. Logically, if your lights are switched on and your battery is not strong, the lights would become dim when the starter is cranked. You may not even be able to start! Imagine in cold weather, you would need every last ampere to crank that cold engine.